(1) Field of the Invention
The present invention relates to a touch panel input device that is usable in various types of electronic devices, such as an image forming device, a portable information terminal device, or a car-mountable information terminal device.
(2) Description of the Related Art
There are electronic devices that utilize touch panel input devices. Examples of such devices include: image forming devices such as printers and multi-function peripherals (MFPs), portable terminal devices, and car-mountable terminal devices. A typical touch panel input device includes a display panel that displays various types of information, and a touch position detection mechanism that detects a touch position (i.e., a position touched by a user) on a surface of the display panel (referred to in the following as a display surface).
Further, when receiving an instruction from the user, the touch panel input device causes a predetermined image to be displayed on the display surface. The image displayed on the display surface may include images of buttons, icons, or the like for receiving touch operations performed by the user. Such images are referred to in the following as button images. Such button images may be, for example, various buttons displayed in a menu screen or keys of a so-called software keyboard displayed on the display surface.
When a button image is displayed on the display surface and a touch position is detected by the touch position detection mechanism at a position on the display surface at which the button image is displayed, input of information allocated in advance to the button image, which may be an instruction to commence copying for example, is received.
Recently, such touch panel input devices are provided with display panels of relatively large sizes. Providing display panels with large sizes is beneficial for users, due to usability, visual perceptibility, etc., being improved. However, providing display panels with large sizes not only increases power consumption of the display panel, but also increases power consumption of the touch position detection mechanism. Thus, there is a demand for technology reducing overall power consumption of touch panel input devices, even in touch panel input devices having display panels of large sizes.
Japanese Patent Application Publication No. 2012-047980 discloses an image forming device including a touch panel that has a liquid crystal display unit and a light source unit (a backlight) that emits light with respect to the liquid crystal display unit.
Due to the light source unit emitting light with respect to the liquid crystal display unit, images indicating various configuration items, such as paper size, images of keys for selecting the configuration items, etc., are displayed on a display surface.
In the image forming device disclosed by Japanese Patent Application Publication No. 2012-047980, when a touch position detection mechanism has detected selection of a configuration item for only a small number of times, the backlight is controlled to emit light with reduced luminance with respect to displayed images of the configuration item and the key for selecting the configuration item. Thus, the power consumption of the backlight is reduced.
However, unfortunately, the technology disclosed in Japanese Patent Application Publication No. 2012-047980 reduces power consumption of the liquid crystal display unit but does not reduce power consumption of the touch position detection mechanism.
Meanwhile, a touch panel input device including a display panel not having a backlight, which is starting to gain popularity, and a touch position detection mechanism attached to such a display panel further reduces power consumption compared to touch panel input devices including backlights. However, as display panels in such touch panel input devices become greater in size and higher in definition, power consumption of touch position detection mechanisms increases accordingly. This increase in power consumption of touch position detection mechanisms cannot be ignored, and thus, necessitates improvement.